In order for embryonic development to proceed correctly and reproducibly, the expression of genes in individual cells of an embryo must be coordinated with precision. One way in which temporal and spatial coordination of gene expression is achieved is through the action of transcription factors, proteins which bind to DNA and regulate expression of specific target genes. In Drosophila embryos, the maternally provided transcription factor Bicoid (Bcd) provides the positional information to pattern the anterior-posterior (AP) axis of the embryo. Bcd protein diffuses from the anterior pole of the embryo and is known to bind to over 1000 sites in the genome, thereby activating at least twenty target genes at different positions along the AP axis. A traditional model suggests the positional information in an embryo is a direct readout of Bcd concentration. Although recent studies have challenged this model, the mechanistic relationship between local Bcd concentration, DNA binding, and target gene expression is unknown. The experiments proposed here aim to directly measure the in vivo concentration-dependence of Bcd DNA binding and target gene expression. This work will elucidate the effects of protein concentration on the ability of transcription factors to control the expression of their targets.